Application of direct stochastic optical reconstruction microscopy (dSTORM) to the histological analysis of human glomerular disease

Electron microscopy (EM) following immunofluorescence (IF) imaging is a vital tool for the diagnosis of human glomerular diseases, but the implementation of EM is limited to specialised institutions and it is not available in many countries. Recent progress in fluorescence microscopy now enables conventional widefield fluorescence microscopes to be adapted at modest cost to provide resolution below 50 nm in biological specimens. We show that stochastically switched single-molecule localisation microscopy can be applied to clinical histological sections stained with standard IF techniques and that such super-resolved IF may provide an alternative means to resolve ultrastructure to aid the diagnosis of kidney disease where EM is not available. We have implemented the direct stochastic optical reconstruction microscopy technique with human kidney biopsy frozen sections stained with clinically approved immunofluorescent probes for the basal laminae and immunoglobulin G deposits. Using cases of membranous glomerulonephritis, thin basement membrane lesion, and lupus nephritis, we compare this approach to clinical EM images and demonstrate enhanced imaging compared to conventional IF microscopy. With minor modifications in established IF protocols of clinical frozen renal biopsies, we believe the cost-effective adaptation of conventional widefield microscopes can be widely implemented to provide super-resolved image information to aid diagnosis of human glomerular disease.

Optical sectioning microscopes with no moving parts using a micro-stripe array light emitting diode

We describe an optical sectioning microscopy system with no moving parts based on a micro-structured stripe-array light emitting diode (LED). By projecting arbitrary line or grid patterns onto the object, we are able to implement a variety of optical sectioning microscopy techniques such as grid-projection structured illumination and line scanning confocal microscopy, switching from one imaging technique to another without modifying the microscope setup. The micro-structured LED and driver are detailed and depth discrimination capabilities are measured and calculated.

Time-domain whole-field fluorescence lifetime imaging with optical sectioning

A whole-field time-domain fluorescence lifetime imaging (FLIM) microscope with the capability to perform optical sectioning is described. The excitation source is a mode-locked Ti:Sapphire laser that is regeneratively amplified and frequency doubled to 415 nm. Time-gated fluorescence intensity images at increasing delays after excitation are acquired using a gated microchannel plate image intensifier combined with an intensified CCD camera. By fitting a single or multiple exponential decay to each pixel in the field of view of the time-gated images, 2-D FLIM maps are obtained for each component of the fluorescence lifetime. This FLIM instrument was demonstrated to exhibit a temporal discrimination of better than 10 ps. It has been applied to chemically specific imaging, quantitative imaging of concentration ratios of mixed fluorophores and quantitative imaging of perturbations to fluorophore environment. Initially, standard fluorescent dyes were studied and then this FLIM microscope was applied to the imaging of biological tissue, successfully contrasting different tissues and different states of tissue using autofluorescence. To demonstrate the potential for real-world applications, the FLIM microscope has been configured using potentially compact, portable and low cost all-solid-state diode-pumped laser technology. Whole-field FLIM with optical sectioning (3D FLIM) has been realized using a structured illumination technique.

Whole-field five-dimensional fluorescence microscopy combining lifetime and spectral resolution with optical sectioning

We report a novel whole-field three-dimensional fluorescence lifetime imaging microscope that incoporates multispectral imaging to provide five-dimensional (5-D) fluorescence microscopy. This instrument, which can acquire a 5-D data set in less than a minute, is based on potentially compact and inexpensive diode-pumped solid-state laser technology. We demonstrate that spectral discrimination as well as optical sectioning minimize artifacts in lifetime determination and illustrate how spectral discrimination improves the lifetime contrast of biological tissue.

Adaptive aberration correction in a two-photon microscope

We demonstrate aberration correction in two-photon microscopy. Specimen-induced aberrations were measured with a modal wavefront sensor, implemented using a ferro-electric liquid crystal spatial light modulator (FLCSLM). Wavefront correction was performed using the same FLCSLM. Axial scanned (xz) images of fluorescently labelled polystyrene beads using an oil immersion lens show restored sectioning ability at a depth of 28 &mgr;m in an aqueous specimen.

Whole-field optically sectioned fluorescence lifetime imaging

We describe a novel three-dimensional fluorescence lifetime imaging microscope that exploits structured illumination to achieve whole-field sectioned fluorescence lifetime images with a spatial resolution of a few micrometers.

Closed-loop aberration correction by use of a modal Zernike wave-front sensor

We describe the practical implementation of a closed-loop adaptive-optics system incorporating a novel modal wave-front sensor. The sensor consists of a static binary-phase computer-generated holographic element, which generates a pattern of spots in a detector plane. Intensity differences between symmetric pairs of these spots give a direct measure of the Zernike mode amplitudes that are present in the input wave front. We use a ferroelectric liquid-crystal spatial light modulator in conjunction with a 4-f system and a spatial filter as a wave-front correction element. We present results showing a rapid increase in Strehl ratio and focal spot quality as the system corrects for deliberately introduced aberrations.

New modal wave-front sensor: a theoretical analysis

We present a new design of a modal wave-front sensor capable of measuring directly the Zernike components of an aberrated wave front. The sensor shows good linearity for small aberration amplitudes and is particularly suitable for integration in a closed-loop adaptive system. We introduce a sensitivity matrix and show that it is sparse, and we derive conditions specifying which elements are necessarily zero. The sensor may be temporally or spatially multiplexed, the former using a reconfigurable optical element, the latter using a numerically optimized binary optical element. Different optimization schemes are discussed, and their performance is compared.

A wavefront generator for complex pupil function synthesis and point spread function engineering

We describe a simple method to produce an arbitrary complex optical field using a ferroelectric liquid crystal spatial light modulator. The system is configured so as to act as a pupil plane filter in a confocal microscope. The ability to tune the complex pupil function permits the system to be used both to modify the imaging performance by effectively engineering the point spread function as well as to remove optical aberrations present in the optical system.

Optimized pupil-plane filters for confocal microscope point-spread function engineering

We present a new method of superresolving pupil-plane filter design in confocal microscopy in which we specify the properties of the desired point-spread function and use an optimization procedure to determine a suitable pupil-plane filter. A new, flexible method of filter implementation using reconfigurable binary optical elements is described, and experimental results are presented.

Wide-field optically sectioning fluorescence microscopy with laser illumination

We describe an extremely simple method by which optically sectioned fluorescence images may be obtained with conventional microscopes using laser illumination. A one-dimensional grid pattern is introduced into the illumination system, together with a rotating ground glass diffuser. This causes an image of the grid pattern to be projected into the specimen. Images taken at three spatial positions of the grid are processed in a simple manner to provide optically sectioned images of fluorescent specimens.

Dynamic wave-front generation for the characterization and testing of optical systems

We describe a simple method for generating known optical aberrations dynamically, using a ferroelectric liquid-crystal spatial light modulator. Aberrations inherent in the optical system are measured and corrected, and as an example Kolmogorov turbulence is simulated for aperture sizes D/r(0) from 0 to 30, varying at frame rates up to 2.5 kHz. A measure of wave-front generation efficiency is introduced and is shown to be better than 86% for Kolmogorov phase screens with D/r(0) in the range from 0 to 30.

Real-time three-dimensional imaging of macroscopic structures

We describe an extremely simple method of obtaining optically sectioned images with conventional low-power imaging systems in real time. A single spatial frequency grid pattern is projected onto an object. Images taken at three spatial positions of the grid projection are processed to provide 3D images of macroscopic structures.

Method of obtaining optical sectioning by using structured light in a conventional microscope

We describe a simple method of obtaining optical sectioning in a conventional wide-field microscope by projecting a single-spatial-frequency grid pattern onto the object. Images taken at three spatial positions of the grid are processed in real time to produce optically sectioned images that are substantially similar to those obtained with confocal microscopes.

Confocal microscopy by aperture correlation

Most confocal microscopes do not produce images in real time with nonlaser light sources. The tandem scanning confocal microscope does produce such images but, because the pinhole apertures of the Nipkov disk must be placed far apart to reduce cross talk between neighboring pinholes, only 1% or less of the light available for imaging is used. We show that, by using aperture correlation techniques and relaxing the requirement to obtain a pure confocal image directly, one can obtain real-time confocal images with a dramatically increased (25% or even 50%) light budget.

Efficient real-time confocal microscopy with white light sources

The main advantage of confocal microscopes over their conventional counterparts arises from their ability to optically 'section' nearly transparent materials; the thin image slices thus obtained can be used to reconstruct three-dimensional images, a capability which is particularly useful for the study of biological specimens. Confocal microscopes have previously used either a single laser-illuminated point-source and single point-detector (which are scanned in tandem across the object) or white-light illumination with multiple point-sources and detectors. Single-point-source systems, however, do not usually form images in real time and are restricted to using available laser wavelengths. Multiple-point-source systems, on the other hand, produce images in real time but use light very inefficiently--typically 1% or less is used for imaging. Here we demonstrate a white-light, multiple-point-source method which can in principle produce images in real time with light efficiencies as high as 50%. This system is likely to find broad practical application, particularly in the imaging of weakly reflecting or weakly fluorescent specimens.

Programmable multiple-level phase modulation that uses ferroelectric liquid-crystal spatial light modulators

We present a novel method of producing arbitrarily valued binary phase-only modulation from a commercially available ferroelectric liquid-crystal spatial light modulator that is used in conjunction with simple polarization components. By cascading of such stages, modulators with four and eight equally spaced phase levels are constructed with 128 × 128 pixels. Near-diffraction-limited performance, when stopped down to 64 × 64 pixels, is reported in producing simple diffraction patterns and when used to generate asymmetric spot arrays in the Fourier plane of a lens.